Color profiling involves the generation of color profiles that characterize the output of color imaging devices using particular print media and colorants. Color profiles can be used to transform color image data for reproduction of color images using different types of color imaging devices.
Different types of imaging devices exhibit varied responses to input color image data. Indeed, color matching has become one of the most challenging problems in the field of color imaging. In response to a given set of input color image data, one type of imaging device may produce color output that is significantly different from the color output produced by another type of imaging device.
For example, the color output of a particular printer may be markedly different from the color output of a display device such as a cathode ray tube (CRT) monitor, even though the devices are presenting the same image. In addition, there may be significant variation among different imaging devices of the same type, such as different printers. Different output media, such as paper or film, and different colorants, such as inks and donor sheets, also contribute to variation.
To achieve more consistent color output among different devices, i.e., color matching, the input color image data can be transformed to compensate for color response differences among different devices. Transformation may involve numeric adjustment of individual color data values contained in the input color image data. The transformation process is sometimes referred to as correction or conversion. The transformation takes into account the individual color response characteristics of a particular imaging device.
Typically, the transformation relies on a source device profile and a destination device profile. A source profile characterizes the color response of a source device, whereas a destination profile characterizes the color response of the destination device. In the case of a printer, the profiles also may correspond to particular combinations of output media and ink. The source device may be an imaging device for which the input color image data was initially formulated. The destination device is the device selected by a user to reproduce the image.
To achieve similar output from the destination device, a color matching module uses the source and destination device profiles to determine the differences between the devices, and develops a mapping, or “link,” that compensates for those differences. In particular, the mapping relates source device coordinates to destination device coordinates, and thereby facilitates transformation of the input color image data. For a display device, the device coordinates may be red, green, and blue (RGB). For a printer, the device coordinates may be cyan, magenta, yellow and black (CMYK).
Generation of color profiles typically involves driving a color imaging device to produce a range of color elements, or “patches,” in response to a set of color image data. In the case of a printer, for example, a range of color patches is printed on a sheet of paper or film. The color profiling process further involves measuring the color elements to produce colorimetric values that characterize the response of the color imaging device to the color image data.